It is well known in the thermal printing art that particles can be used in thermal media to keep the thermal print head free of dirt and debris. The particles are preferably small inorganic particles used in a slipping layer of a dye-donor element and the abrasive action of the particles cleans the thermal print head during the printing operation. Polymethylsilsesquioxane particles, such as Tospearl.RTM. (Toshiba Silicone Co.), have been proposed for use in thermal media as described in copending U.S. Application Ser. No. 081976,772 of Simpson et al., filed Nov. 24, 1997. However, these particles have a very broad particle size distribution